1. Field of the Invention
This invention relates to a TLN signal generating apparatus used in an optical disc drive for playing back or recording and playing back an optical disc and an optical disc drive equipped with the TLN signal generating apparatus, and also relates to an optical disc drive equipped with an amplitude adjusting apparatus for a tracking error signal.
2. Description of the Prior Art
Optical discs including read-only type optical discs such as an audio CD (compact disc) and a CD-ROM and recordable type optical discs such as a CD-R or the like are driven by optical disc drives. These optical disc drives are normally equipped with an optical pick-up which is movable along a radial direction of an optical disc and a sled motor for moving the optical disc in the radial direction thereof.
The optical pick-up includes an optical pick-up body equipped with a laser diode and a split photodiode, an objective lens which is supported by the pick-up body by means of suspension springs so as to be freely movable in the radial direction of the optical disc as well as the rotation axial direction thereof, and an actuator for moving the objective lens in the radial direction as well as the axial direction.
In these optical disc drives, data recorded on the optical disc in a spiral manner is reproduced by moving the optical pick-up in the radial direction so as to follow the track while rotating the optical disc.
When the optical pick-up is to be moved to a predetermined track on the optical disc, a track jump control is carried out. For example, when a predetermined music number (e.g. a third music) is selected, the optical pick-up is moved to the predetermined track automatically through the track jump control, thereby enabling to playback the selected music immediately.
The track jump performed in the optical disc drive generally includes a rough search and a fine search. The rough search is used to jump the optical pick-up to a track which is relatively far away from the present position of the optical pick-up, while the fine search is used to jump the optical pick-up to a relatively close track.
Hereinbelow, an explanation is made with regard to the operation of the fine search. In this connection, FIG. 36 is a schematic drawing which shows pre-grooves (WOBBLE) 131a, 131b formed in an optical disc and lands 132a, 132b formed between of the pre-grooves. Information (data) is recorded in the pre-grooves 131a, 131b, that is pits are formed in the pre-grooves 31a, 131b. 
A laser beam (comprised of a main beam and a sub-beam) which is emitted from the laser diode is reflected on the pre-grooves 131a, 131b and the lands 132a, 132b, and then the reflected beam 133a to 133c is received by the split photodiode and then converted into electrical signals. Various signals such as a track loss signal (hereinafter, referred to as xe2x80x9cTLN signalxe2x80x9d, details of which will be explained later) and a tracking error signal and the like are produced based on the electrical signals produced by the optical pick-up.
When a fine search is to be carried out, the optical pick-up is moved to the radial direction of the optical disc (the direction indicated by the arrow xe2x80x9cYxe2x80x9d in FIG. 36). Therefore, the optical pick-up traverses the pre-grooves and the lands alternately. In this case, as shown in FIG. 37, the TNL signal has a waveform in which the level of the TLN signal S1 raises when the main beam traverses portions defined by the pre-grooves 131a, 131b and the level thereof decreases when the main beam traverses portions defined by the lands 132a, 132b. 
Therefore, when a track jump is to be carried out during the fine search, the number of tracks to be jumped can be obtained by counting peaks of the TLN signal S1. In more details, as shown in FIG. 37, a predetermined reference level L1 is pre-set, and a TLN signal is digitized based on the reference level L1. Then, by counting the number that the digitized TLN signal S1 exceeds the reference level L1, it is possible to carry out a track jump to a predetermined track. For example, in the case where a command that moves the optical pick-up for ten tracks is given, the optical pick-up is being moved until the TLN signal obtained from the received beam exceeds the reference level L1 for ten times.
However, actually, the waveform of the TLN signal S1 does not have the same amplitudes in the up and down directions with respect to the reference level L1, and it has an offset component (direct current component). For this reason, the TLN signal S1 is oscillated with respect to a level L2 which is sifted for a predetermined value from the reference level L1. The offset component varies depending on various factors such as ambient temperature, deterioration due to elapse of time, tilting degree of the optical pick-up (improper skew adjustment), and loading condition of the optical disc or the like. Therefore, in the case where the offset component is large, there is a case that the TLN signal S1 does not exceed (cross) the reference level L1 even though the TLN signal is being actually oscillated. In such a case, it is not possible to digitize the TLN signal correctly. With this result, there arises a problem that it is not possible to move the optical pick-up to the designated track, because any one or more of tracks can not be counted during the fine search even though the optical pick-up has actually traversed them. In particular, in the case of CD-R and CD-RW and the like in which no data has yet been recorded, amplitude of TLN signal obtained therefrom is quite small, so that influence from the offset component contained in the TLN signal is relatively large.
Further, in recent years, various optical discs such as CD-R, CD-ROM, CD-RW have been developed and then widely used. Therefore, it is desired that it is possible to playback and record these optical discs with a single optical disc drive in a compatible manner. However, since the reflectances of the reflective layers of CD-R, CD-ROM and CD-RW are different from each other, the tracking error signals obtained from these optical discs are also different from each other. Further, even among the optical discs of the same type, there is a case that amplitudes of tracking error signals are different from each other due to individual differences of the respective optical discs.
Specifically, in the case where an amplitude of a tracking error signal reproduced from a data disc of CD-R (having pre-pits) is supposed to be 1, an amplitude of a tracking error signal reproduced from a data disc of CD-ROM is approximate to 0.7 and an amplitude of a tracking error signal reproduced from a data disc of CD-WR is approximate to 3.5, respectively. Therefore, if amplitude adjustment would not be performed so as to meet the respective disc, a tracking servo will not be engaged properly, thus making it difficult to perform accurate recording and playing back control.
It is therefore an object of the present invention to provide a TLN signal generating apparatus used in an optical disc drive and an optical disc drive equipped with the apparatus which can accurately and reliably grasp the position of the optical pick up with respect to the optical disc during the movement of the optical pick-up.
It is another object of the present invention to provide an optical disc drive equipped with an amplitude adjusting apparatus for a tracking error signal which can adjust the amplitude of the tracking error signal in an optimum condition irrespective of types of optical discs and individual differences between optical discs.
In order to achieve the object, the present invention is directed to an optical disc drive equipped with a TLN signal generating apparatus, in which the TLN signal generating apparatus comprises:
TLN signal generating means for generating a TLN signal (track loss signal) based on signals obtained from an optical pick-up;
a digitizing circuit for digitizing the TLN signal generated by the TLN signal generating means by comparing it with a reference level; and
correction means for correcting the TLN signal generated by the TLN signal generating means so that it is accurately digitized by the digitizing circuit irrespective of an offset component which is a direct current component contained in the TLN signal.
According to the optical disc drive described above, it is possible to digitize the TLN signal accurately without receiving any influence from the offset component contained in the TLN signal. Therefore, in the case where the optical pick-up is moved to a target track by grasping the radial position of the optical pick-up relative to the optical disc based on the TLN signal, it is possible to accurately count the number of tracks above which the optical pick-up has passed, so that it becomes possible to move the optical pickup to the target track accurately. This is particularly effective where optical discs such as CD-R and CD-RW from which a small amplitude TLN signal is obtained are used.
In this optical disc drive, it is preferred that the correction means includes:
offset component detecting means for detecting a level of the offset component contained in the TLN signal; and
signal control means for controlling, responsive to the level of the offset component detected by the offset component detecting means, a level of the TLN signal generated by the TLN signal generating means so that the level of the TLN signal will become a level which does not receive any influence from the level of the direct component.
Further, in this case, it is more preferable that the signal control means controls, responsive to the level of the offset component detected by the offset component detecting means, a level of the TLN signal generated by the TLN signal generating means so that the offset component is decreased or eliminated.
Furthermore, it is also preferred that the offset component detecting means is constructed so as to detect a peak value and a bottom value of the TLN signal generated by the TLN signal generating means and then obtain the level of the offset component based on the peak and bottom values.
In this case, it is preferred that the offset component detecting means is constructed so as to detect a median value between a peak value and a bottom value of the TLN signal generated by the TLN signal generating means or a value calculated based on the median value as the level of the offset component.
Moreover, it is also preferred that the signal correction means includes a reference voltage output means for outputting a reference voltage used in generating the TLN signal by the TLN signal generating means; and means for variably controlling the reference voltage outputted from the reference voltage output means.
Since the optical disc drive of the present invention controls the level of the TLN signal by adjusting the reference voltage used in generating the TLN signal, it has a good response to fluctuation of the amplitude of the TLN signal.
Further, preferably, the TLN signal generating apparatus can further comprise an optical pick-up driving means for driving and controlling the optical pick-up so that a beam emitted onto the optical disc after a focus servo has been engaged is displaced along the radial direction of the optical disc; and an eccentric component generating means for generating an eccentric component based on the reflected light of the beam obtained when the optical pick-up is controlled and driven by the optical pick-up driving means.
By providing such an eccentric component generating means, it is possible to prevent undesired situation in which a waveform of the TLN signal is expanded (an interval between adjacent waves becomes wide) even in the case where a loaded optical disc has less or no eccentric component. Namely, since the interval of adjacent waves becomes narrow, it is possible to stably hold peaks and bottoms of the TLN signal in the peak/bottom detection circuit. As a result, it becomes possible to accurately and reliably perform the offset adjustment for the TLN signal.
Alternatively, it is also preferred that the correction means includes a signal correcting circuit which amplifies an alternating current component contained in the TLN signal generated by the TLN signal generating means without eliminating a directed current component contained in the TLN signal.
According to this structure, since only the alternating component of the TLN signal is amplified without eliminating a direct current component contained in the TLN signal, it has a good response to the fluctuation on the amplitude of the TLN signal.
In this case, it is preferred that the signal correcting circuit is constructed so as not to eliminate an alternating current component contained in the TLN signal and having a frequency less than a first frequency and the direct current component contained therein, but so as to amplify an alternating current component contained in the TLN signal and having a frequency higher than a second frequency which is higher than the first frequency.
In this case, it is preferred that the signal correcting circuit includes a high boost filter.
Another aspect of the present invention is directed to a TLN signal generating apparatus used in an optical disc drive, in which the TLN signal generating apparatus comprises:
TLN signal generating means for generating a TLN signal (track loss signal) based on signals obtained from an optical pick-up;
offset component detecting means for detecting an offset component (direct current component) contained in the TLN signal generated by the TLN signal generating means;
signal control means for controlling, responsive to a level of the offset component detected by the offset component detecting means, a level of the TLN signal generated by the TLN signal generating means so that the offset component in the TLN signal is reduced or eliminated therefrom; and
a digitizing circuit for digitizing the TLN signal which has been corrected by the signal control means by comparing it with a reference level.
In this case, it is preferred that the offset component detecting means is constructed so as to detect a peak value and a bottom value of the TLN signal generated by the TLN signal generating means and then obtain the level of the offset component based on the peak and bottom values.
Further, it is also preferred that the offset component detecting means is constructed so as to detect a median value between a peak value and a bottom value of the TLN signal generated by the TLN signal generating means or a value calculated based on the median value as the level of the offset component.
Furthermore, it is also preferred that the signal correction means includes a reference voltage output means for outputting a reference voltage used in generating the TLN signal by the TLN signal generating means; and means for variably controlling the reference voltage outputted from the reference voltage output means.
Preferably, the TLN signal generating apparatus can further comprise an optical pick-up driving means for driving and controlling the optical pick-up so that a beam emitted onto the optical disc after a focus servo has been engaged is displaced along the radial direction of the optical disc; and an eccentric component generating means for generating an eccentric component based on the reflected light of the beam obtained when the optical pick-up is controlled and driven by the optical pick-up driving means.
The other aspect of the present invention is directed to a TLN signal generating apparatus used in an optical disc drive, in which TLN signal generating apparatus comprises:
TLN signal generating means for generating a TLN signal (track loss signal) based on signals obtained from an optical pick-up;
a signal correcting circuit which amplifies an alternating current component contained in the TLN signal generated by the TLN signal generating means without eliminating a directed current component contained in the TLN signal; and
a digitizing circuit for digitizing the TLN signal which has been corrected by the signal correcting circuit by comparing it with a reference level.
In this TLN signal generating apparatus, it is preferred that the signal correcting circuit is constructed so as not to eliminate an alternating current component contained in the TLN signal and having a frequency less than a first frequency and the direct current component contained therein, but so as to amplify an alternating current component contained in the TLN signal and having a frequency higher than a second frequency which is higher than the first frequency.
In this case, it is preferred that the signal correcting circuit includes a high boost filter.
Further, preferably, the TLN signal generating apparatus can further comprise an optical pick-up driving means for driving and controlling the optical pick-up so that a beam emitted onto the optical disc after a focus servo has been engaged is displaced along the radial direction of the optical disc; and an eccentric component generating means for generating an eccentric component based on the reflected light of the beam obtained when the optical pick-up is controlled and driven by the optical pick-up driving means.
Other aspect of the present invention is directed to an optical disc drive having an amplitude adjusting apparatus for a tracking error signal, in which the amplitude adjusting apparatus comprises:
amplifying means for amplifying a tracking error signal generated based on a signal obtained from an optical pick-up with a variable amplification factor;
amplification value detecting means for detecting an amplification value of the tracking error signal from the amplifying means; and
means for variably controlling the amplification factor of the amplifying means so that the amplification value detected by the amplification value detecting means becomes substantially coincide with a reference amplification value which is used as a reference level of the tracking error signal by comparing the amplification value detected by the amplification value detecting means with the reference level of the tracking error signal.
According to the optical disc drive equipped with the amplitude adjusting apparatus described above, it is possible to adjust the value of the amplitude in a constant value irrespective of types of optical discs and individual differences between the same type optical discs. This makes it possible to hold a gain in the tracking servo constant and to obtain stability in the tracking servo operation.
In this case, it is preferred that the amplification factor controlling means of the amplitude adjusting apparatus is adapted to variably control the amplification factor in the amplifying means so that the amplification value of the tracking error signal is substantially coincide with the reference level in the case where the amplification value detected by the amplification value detecting means is less than the reference level.
Further, it is more preferable that the amplification factor controlling means of the amplitude adjusting apparatus is constructed so as to detect a difference between a peak value and a bottom value of the tracking error signal obtained from the amplifying means as the amplification value of the tracking error signal.
Furthermore, preferably, the amplitude adjusting apparatus can further comprise an optical pick-up driving means for driving and controlling the optical pick-up so that a beam emitted onto the optical disc after a focus servo has been engaged is displaced along the radial direction of the optical disc; and an eccentric component generating means for generating an eccentric component based on the reflected light of the beam obtained when the optical pick-up is controlled and driven by the optical pick-up driving means.
By providing such an eccentric component generating means, it is possible to prevent undesired situation in which a waveform of the tracking error signal is expanded (an interval between adjacent waves becomes wide) even in the case where a loaded optical disc has less or no eccentric component. Namely, since the interval of adjacent waves becomes narrow, it is possible to stably hold peaks and bottoms of the tracking error signal in the peak/bottom detection circuit. As a result, it becomes possible to accurately and reliably perform the amplitude adjustment for the tracking error signal.